Can a python script execute a function inside a bash script?

Question

I have a bash script provided by a 3rd party which defines a set of functions. Here's a template of what that looks like

$ cat test.sh

#!/bin/bash

define go() {
    echo "hello"
}

I can do the following from a bash shell to call go():

$ source test.sh
$ go
hello

Is there any way to access the same function from a python script? I tried the following, but it didn't work:

Python 2.6.6 (r266:84292, Sep 15 2010, 15:52:39) 
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import subprocess
>>> subprocess.call("source test.sh")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.6/subprocess.py", line 470, in call
    return Popen(*popenargs, **kwargs).wait()
  File "/usr/lib/python2.6/subprocess.py", line 623, in __init__
    errread, errwrite)
  File "/usr/lib/python2.6/subprocess.py", line 1141, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory
>>>

What function is it in bash that you can't duplicate in Python? — ghostdog74
– ghostdog74, Commented Apr 29, 2011 at 0:18

samplebias · Accepted Answer · 2011-04-29 00:21:27Z

44

Yes, indirectly. Given this foo.sh:

function go() { 
    echo "hi" 
}

Try this:

>>> subprocess.Popen(['bash', '-c', '. foo.sh; go'])

Output:

hi

edited Apr 29, 2011 at 0:21

answered Apr 29, 2011 at 0:16

samplebias

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Samuel · Accepted Answer · 2017-10-16 10:55:23Z

2

Based on @samplebias solution but with some modification that worked for me,

So I wrapped it into function that loads bash script file, executes bash function and returns output

def run_bash_function(library_path, function_name, params):
    params = shlex.split('"source %s; %s %s"' % (library_path, function_name, params))
    cmdline = ['bash', '-c'] + params
    p = subprocess.Popen(cmdline,
                         stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    stdout, stderr = p.communicate()
    if p.returncode != 0:
        raise RuntimeError("'%s' failed, error code: '%s', stdout: '%s', stderr: '%s'" % (
            ' '.join(cmdline), p.returncode, stdout.rstrip(), stderr.rstrip()))
    return stdout.strip()  # This is the stdout from the shell command

edited Oct 16, 2017 at 10:55

answered Oct 7, 2015 at 16:23

Samuel

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6 Comments

donkopotamus Over a year ago

If you're writing a function to take arbitrary parameters, then you should be using shlex.quote.

Samuel Over a year ago

@donkopotamus Correct, but I think shlex.split will do the work in that case, isn't it? i.e: shlex.split('"source %s; %s %s"' % (library_path, function_name, params))

donkopotamus Over a year ago

There's no mention of shlex.split in your answer. In any case, shlex.split does not handle quoting inputs. The point is the following ... what will your function do if called with a function name of blah; rm -rf /? (I wouldn't recommend you test it ...)

Samuel Over a year ago

@donkopotamus, Still didn't get your point though. If user decides to call rm -fr / instead of calling actual function it his own fault. BTW, "blah" is not a function name but path to libray from where the function loaded

donkopotamus Over a year ago

Yes, that was a typo ... I'm aware blah is a filename. Filenames can be anything ... they should be quoted before passing to a shell in case they contain characters that mean something to the shell. Those characters could be as simple as a space, or as foolish as a semicolon.

|

theduke · Accepted Answer · 2011-04-29 00:32:36Z

1

No, the function is only available within that bash script.

What you could do is adapt the bash script by checking for an argument and execute functions if a specific argument is given.

For example

# $1 is the first argument

case $1 in
 "go" )
       go
       ;;
 "otherfunc" )
       otherfunc
       ;;
 * )
       echo "Unknown function"
       ;;
esac

Then you can call the function like this:

subprocess.call("test.sh otherfunc")

edited Apr 29, 2011 at 0:32

answered Apr 29, 2011 at 0:06

theduke

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